Flexography
Flexography (often abbreviated to flexo) is a form of printing process which utilizes a flexible relief plate.
It is essentially a modern version of letterpress, evolved with high speed rotary functionality, which can be used for printing on almost any type of substrate, including plastic, metallic films, cellophane, and paper.
In the early 1900s, other European presses using rubber printing plates and aniline oil-based ink were developed.
Laser-etched ceramic anilox rolls along with chambered ink systems, have also played a part in the improvement of print quality.
Full-color picture printing is now possible, and some of the finer presses available today, in combination with a skilled operator, allow quality that rivals the lithographic process.
One ongoing improvement has been the increasing ability to reproduce highlight tonal values, thereby providing a workaround for the very high dot gain associated with flexographic printing.
After addition of absorb gelatine for example, the photopolymer residue can be disposed of as standard solid waste together with household refuse.
Companies such as AV Flexologic, Glunz & Jensen, XSYS, Esko, Kodak, Polymount, Screen and SPGPrints from The Netherlands are market leaders in manufacturing this type of equipment.
The first step is to create a metal plate out of the negative of our initial image through an exposition process (followed by an acid bath).
Special machinery is made for mounting these plates on the printing cylinders to maintain registration.
Earle L. Harley invented and patent the Opti-Chek Mounting and Proofing machine enabling the operator to check the registration before going to the press.
Precision mounting is critical for producing good quality print which is in the register and has a direct impact on minimizing waste.
Positioning is achieved by correctly lining up register marks that are common to each plate in the set.
Types of registration marks These are various types of mark used for aligning the plates correctly: Registration crosses are commonly used but need to be positioned in waste areas as they are easily seen on the print, they can also be used as a guide for aligning the print to a bag or box structure if this is required.
On most mounting machines the dots or crosses on the plates are lined up using magnifying cameras, the higher the magnification the greater the accuracy.
Register crosses are more common in label and corrugated printing where waste and hidden folds are normal, the microdot is common in flexible packaging where waste is kept to a minimum and no un-required marks are to be seen on the packaging (example meat, dairy and hygiene).
It is also recommended to have two more pairs, one at either end so a simple rotation and check under the cameras confirms the plate has not twisted when it was laid/stuck down.
To step plates around the sleeve to minimise risk of bounce is done either mechanically using an index disc or by use of stepper motors to drive and lock it in position.
The cameras provide an enlarged visual display indicating whether or not the register marks are correctly positioned in line with crosshair targets.
[5] In recent years higher quality demands from customers, shorter and more frequent job runs result in an increasing relative cost of the prepress department.
Then it transfers to the anilox or ceramic roll (or meter roll) whose texture holds a specific amount of ink since it is covered with thousands of small wells or cups that enable it to meter ink to the printing plate in a uniform thickness evenly and quickly (the number of cells per linear inch can vary according to the type of print job and the quality required).
[6] To avoid getting a final product with a smudgy or lumpy look, it must be ensured that the amount of ink on the printing plate is not excessive.
The anilox roller transfers a uniform thickness of ink to a flexible printing plate.
Flexographic printing inks are primarily formulated to remain compatible with the wide variety of substrates used in the process.
Each formulation component individually fulfills a special function and the proportion and composition will vary according to the substrate.
This system is best used for low quality print such as flood coats and block lettering due to its inability to produce a clean wipe of the anilox roll.
The cylinder plate, anilox, and doctor blade are independently controlled by hydraulic, pressure and/or pneumatic systems.
This system is best used for high quality, intricate print designs, like those found in the label industry.
Flexo has an advantage over lithography in that it can use a wider range of inks, water based rather than oil based inks, and is good at printing on a variety of different materials like plastic, foil, acetate film, brown paper, and other materials used in packaging.
Typical products printed using flexography include brown corrugated boxes, flexible packaging including retail and shopping bags, food and hygiene bags and sacks, milk and beverage cartons, flexible plastics, self-adhesive labels, disposable cups and containers, envelopes and wallpaper.
